Conventional surface mining systems have devastating environmental results. In hilly or mountainous regions, surface contour mining is accomplished by removing timber and clearing the area to be mined, making a strip cut to form a substantially horizontal bench and a vertical highwall that exposes the seam of mineral deposits to be removed. Another technique is to simply remove the entire top portion of the mountain to extract the minerals deposited below.
Underground mining systems are less damaging to the environment, but more costly and inefficient with lower production rates. When underground mining systems are used to extract mineral or coal deposits from a mineral or coal reserve 10, the reserve 10 is divided into panels 12 as shown in FIG. 1 which are laid out and developed for both shortwall mining and longwall mining operations. Coal reserves conducive to mining adjacent parallel panels (Panels 1 to 8 as shown in FIG. 1) are most desirable because they facilitate panel development and allow shorter equipment moves. As can be seen, the panels 12 are generally rectangular in shape having gate entries 14 (a headgate and tailgate) extending along each length, and are all connected at one end by main entries 16. In modern mining systems, these panels 12 are developed using continuous miner units. In modern longwall mining systems, panels typically range from 400 to 1200 feet in width and from 4,000 to 15,000 feet in length. In modern shortwall mining systems, the shortwall panels typically range from 100 to 200 feet in width and from 2,000 to 4,000 feet in length. Production of coal or other sedimentary deposits begins at one end of the panel 12, the starter entry 18, to mine the seam along its face or wall in the direction indicated by the arrow 19.
Referring more specifically to FIG. 2, panel 1 of FIG. 1 is shown in more detail as panel 20 having headgate entries 22a-c, collectively the headgate 22, and the tailgate entries 24a-c, collectively the tailgate 24, referred to above. While the direction of mining proceeds in the direction indicated by the arrow 19, production or plowing of the coal always proceeds from the headgate 22 to the tailgate 24 in the direction shown by the arrow 25 for both longwall and shortwall mining systems as will be described below in more detail. A “three-entry” development system utilizes the three maingate entries 16a-c, collectively the maingate 16, the three headgate entries 22a-c, and the three tailgate entries 24a-c that are commonly used to provide the necessary airways and escapeways and other functions. The system permits installation of belt and track in the center entry, and allows one outer entry to be used as a return airway. This system is complex and expensive to develop, and is well-known in the mining business.
Upon completing development of the panels 12, the longwall or shortwall mining of the panel 20 commences as shown in FIGS. 3 and 4, respectively. Referring more specifically to FIG. 3, longwall machinery 30 and miners are protected by roof supports 32, 33 designed to withstand tremendous overburden pressures. The material containing the minerals is cut from the face of the seam by a plough or shearer 34 of the longwall machinery 30 and drops onto an armored chain conveyor system (not shown) for transport to a main conveyor system 36, which in turn transports the material to the surface. As successive cuts are made along the face of the seam from the headgate 22 to the tailgate 24 in the direction of production indicated by the arrow 25, the roof supports 32, 33 and armored chain conveyor are advanced into the seam in the direction of mining indicated by the arrow 19, allowing the overburden to collapse or cave-in behind the roof supports 32,33 to form what is known as a gob 38 of loosely-packed material. The roof supports 32,33 not only advance in the mining direction, but also are extendable as known in the art with the supports 32 being shown in the extended configuration and the supports 33 being shown in the retracted configuration.
Referring more specifically to FIG. 4, shortwall machinery 40 and miners are also protected by roof supports 42,43 designed to withstand tremendous overburden pressures. Unlike the longwall miner which ploughs the seam parallel to its face, a shortwall miner cutting head 44 of the shortwall machinery 40 which is approximately 10 to 12 feet in width plows in a direction generally perpendicular to the face of the seam and drops the material onto an armored chain conveyor system (not shown) or mobile shuttle cars for transport to a main conveyor systems 46, which in turn transports the material to the surface. As successive cuts are made along the face of the seam from the headgate 22 to the tailgate 24 in the direction of production indicated by the arrow 25, the roof supports 42,43 and armored chain conveyor are advanced into the seam in the direction of mining indicated by the arrow 19, allowing the overburden to collapse or cave behind the roof supports 42,43 forming the gob 48. The roof supports not only advance in the mining direction as shown by supports 42a and 42b, but also are extendable as known in the art with supports 42 being shown in the extended configuration and supports 43 being shown in the retracted configuration. The shortwall mining system requires significantly less capital and is more flexible in handling geological conditions that vary through the mineral reserve. The only significant disadvantage of the shortwall mining system is that the production rate is somewhat lower as compared to the longwall mining system.
It should be apparent from the above, the primary problem associated with underground longwall and shortwall mining systems is the cost and time associated with developing and creating the panels, and then moving either system from panel to panel underground to mine the entire mineral reserve 10. The moves from panel to panel result in many days of downtime at a high cost to the mining operation. The ingress and egress entries and ventilation associated with the system are all expensive. Time travel to the seam face for the miners is also a significant cost associated with these systems.
Moreover, federal legislation (e.g., Clean Water Act) restricts the use of waste rock produced by large scale surface mining systems as “fill material” legitimately disposed of at other locations. Recent court decisions have held that excess spoil generated by mining operations is waste that does not qualify as fill material that can disposed of as valley fills. Thus, the disposal of excess spoil is a significant problem.
Finally, certain mining areas may have property limitations, such that only one side of the mining area is controlled through lease or ownership, while the other side of the mining area is not controlled. This creates a tremendous burden on miners who wish to utilize mineral reserves under their control.